An Odour that does not Lie

Mikhail P. MOSHKIN, Liudmila A. GERLINSKAYA and Riochi NAGATOMI

Not so long ago it was found that infected males of different animal species display altered signals used for sexual advertising in the "fianc fair" (Hamilton, Zuk, 1982). Importantly, this effect is observed even when an infection is not obvious. Bright colours of fish and birds become paler, bird songs sound poorer and duller. Scent of infected rodent males becomes less attractive for females as compared to the one of their healthy rivals.

The decreased attractiveness of contagious sexual partners is of clear benefit for a population, since probability of spreading pathogens through sexual intercourse is consequently diminished. This serves as a general restriction of reproductive success for the individuals with immune mechanisms compromised by an infection. But is there any benefit for the infected males? One can ask if it is possible to explain the "evasion" of infected males from reproductive competition entirely within the Darwinian paradigm of the intra-species struggle as the basis for evolution, and completely avoiding ethical and moral concepts. In other words, is it of any benefit to be honest?

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